ABCG2 and neoplasm: CSCs of various tumors can commonly express certain cell surface antigenic markers (such as CD133, CD90, CD44, ABCG2, etc.)or transcription factors (such as Oct-3/4, Nanog, Sox2, nestin, c-myc, c-kit, β-catenin, etc.), but the expression levels or amount of these parameters vary greatly among different tumor tissues.